This invention relates to a blow molding method and a blow molding apparatus which are capable of achieving blow molding efficiently with a relatively few molds, cooling blow molding products efficiently in a short period of time, performing a series of blow molding processes including takeout of products and attaching of labels to the molds efficiently, and coping with a variety of production styles ranging from a small scale production to a large scale production.
Blow molding is a popular method for forming hollow containers. In blow molding, a parison extruded from a die head is received by an opened pair of mold pieces of a split mold, the split mold is closed and air is blown into the parison and then the split mold is opened to take out a product.
Blow molding apparatuses for performing such blow molding are generally classified by a manner of moving of split molds into a rotary type blow molding apparatus in which split molds are moved in a circle and a shuttle type blow molding apparatus in which split molds are reciprocated linearly.
In the rotary type blow molding apparatus, split molds mounted on an annular rail are moved in a circle and are opened and closed continuously, whereby blow molding and delivery of a product are completed in one cycle of movement of each split mold on the annular rail.
In the shuttle type blow molding apparatus, two pairs of split molds which reciprocate linearly are provided and these split molds are alternately reciprocated for receiving parisons and for blow molding the parisons.
Accordingly, in a case where a single type of hollow container should be produced in a large scale, the rotary type blow molding apparatus may preferably be employed so that blow molding will be performed efficiently by using a relatively large number, for example 12 to 14, of split molds arranged in a circle.
The shuttle type blow molding apparatus which performs blow molding by alternate reciprocating movement of the two split molds is limited in its blow molding capacity even if the speed of reciprocating movement is increased and, for this reason, is not suitable for a large scale production but suitable for a small scale production.
In a case where a small scale production of various types of products is required for coping with requirement for various types of hollow containers, the rotary type blow molding apparatus has the disadvantage that split molds which are mounted on the apparatus in a set of 12 to 14 split molds must be changed and this takes much time and further it is costly to produce so many split molds.
The shuttle type blow molding apparatus is suitable for such small scale production of various types of products in that change of split molds does not take much time because the number of split molds used is small and the manufacturing cost of split molds is relatively small. The shuttle type blow molding apparatus, however, is limited in its blow molding capacity in a case where a large scale production is required.
There are many cases where a label must be attached to a product which has been produced by blow molding and, in such cases, a label is generally attached to a product simultaneously with performing of blow molding. For this purpose, a product is taken out of an opened split mold after blow molding by means of a product takeout robot and thereafter a label is attached to the split mold by means of a label attaching robot. Thus, two different robots are required and, since it takes a long cycle time for operating these robots, an efficient blow molding cannot be achieved.
Further, the cycle time of the operation of the robots is determined by speed of cooling in blow molding. Cooling of the inside of a parison is difficult when a label is attached so that improvement in efficiency in cooling is desired for.
Furthermore, a product taken out of a split mold generally has flash and, therefore, a step using a device for removing flash from the product becomes necessary for obtaining a final product by blow molding.
It is, therefore, an object of the invention to provide a blow molding method and a blow molding apparatus which are capable of performing blow molding efficiently with a relatively few split molds.
It is another object of the invention to provide a blow molding method and a blow molding apparatus which are capable of cooling a product efficiently in a short period of time.
It is another object of the invention to provide a blow molding method and a blow molding apparatus which are capable of efficiently performing a series of blow molding operations including taking out of a product and attaching of a label to a split mold.
It is still another object of the invention to provide a blow molding method and a blow molding apparatus which are capable of performing blow molding efficiently both in a small scale production and in a large scale production.